The development of splitting tensile strenght (EN 12350-6), measured at 0.5, 1, 2, 3, 7, and 28 days, of all concrete types is shown below as average of two measurements at each age.
The trends observed are much the same as what was evident for the development of compressive strength. Among the Portland cement based concretes it is observed that microsilica apparently increases strength development in the middle period, i.e. particularly from 3 until 28 days of maturity. There is no apparently “kick” in strength development from fly ash at later ages. The slag based concretes exhibit a slow early strength development followed by a period (2-28 days), where the rate of strength gain is significantly higher compared to Portland cement based concrete, before leveling off at a level higher than any of the Portland cement based concretes. For the 3-powder concretes lowering the w/c-ratio from 0.40 to 0.35 results in higher strengths at all ages, while increasing the w/c-ratio from 0.40 to 0.45 results in lower strengths at early and late ages.